1. Field of the Invention
The present invention relates to improvements in an organic light emitting display panel having one or more pixel circuits that includes an organic light emitting diode (OLED) disposed within the pixel circuit, and to improvements in methods of driving the organic light emitting display panel. In particular, the present invention provides an improved pixel circuit with respect to the organic light emitting display panel having an improved gray scale, and an improved driving method for optimally driving the pixel circuit for improving the gray scale.
2. Related Art
A cathode ray tube (CRT) has long been the display device for displaying images on a television. In a CRT display, a gun fires a beam of negatively-charged particles (electrons) inside a large glass tube. The electrons excite phosphor atoms along the wide end of the tube, which causes the phosphor atoms to light up. The video image is produced by lighting up different areas of the phosphor coating with different colors at different intensities. Although the CRT has long been used to display video images, it is bulky. In other words, it order to increase the screen width in a CRT display, the length of the tube must be increased as well in order to give the scanning electron gun room to reach all parts of the screen. Consequently, a CRT having a big screen is heavy and takes up a sizeable space.
A liquid-crystal display (LCD) device is another display device for displaying images. In a conventional LCD device, a built-in backlight is either disposed beside or behind the LCD display. This additional built-in backlight causes the LCD display device to be thick and heavy.
Accordingly, the conventional OLED display panel was introduced to overcome some of the drawbacks of the CRT and LCD display devices. Specifically, the conventional OLED display device includes one or more OLED that can spontaneously emit light without the need to have a built-in backlight. In addition, the conventional OLED provides a large and thin display screen with an image quality and performance equal to or superior to the CRT and/or LCD display device.
The conventional OLED display panel employs a voltage driver to directly modulate the gate voltage of a current source transistor by a voltage signal. However, the voltage driven approach encounters problems with respect to the brightness and/or the gray scale of the OLED. Accordingly, there is a need to have an OLED pixel circuit that improves the gray scale as well as improving the brightness of the OLED. In addition, there is also a need to provide a method of employing a current driver to drive currents to the OLED.